I know that it has an elementary abelian normal subgroup of order 64...

But when I try to find it, this happens..

gap> n := NormalSubgroups(g);
Error <obj> is not a subset of the parent of <G> at
Error( "<obj> is not a subset of the parent of <G>" );
ClosureSubgroup( b, k ) called from
SubgroupsSolvableGroup( r, rec(
actions := auts,
funcnorm := r,
consider := ExactSizeConsiderFunction( Index( j, M ) ),
normal := true ) ) called from
<function>( <arguments> ) called from read-eval-loop
Entering break read-eval-print loop, you can 'quit;' to quit to outer
loop,
or you can return to continue

What am I doing wrong? I read the manual, but cannot see any
pre-conditions
for the "NormalSubgroups" routine that I am violating...